Yersinia pestis is a Gram-negative bacterial human pathogen that is the causative agent of plague. Historically Y. pestis has been responsible for significant human morbidity and mortality. Due to the high mortality rates and severe disease caused by Y. pestis, it has emerged as an agent of biological warfare and bioterrorism. A more detailed understanding of the pathogenesis of Y. pestis will facilitate the identification of targets for vaccine development and treatment. Currently, aside from studies of the type III secretion system and effectors encoded on the virulence plasmid, very little is known about the pathogenesis of Y. pestis at the molecular level. Much of what is known about the pathogenesis of Yersiniae comes from the investigation of the other two human pathogens in the genus, Y. enterocolitica and Y. pseudotuberculosis, both of which are primarily enteric pathogens but are capable of causing systemic infection much like Y. pestis. The enteropathogenic Yersiniae are some of the best-characterized pathogens due to the ease of genetic manipulation and the use of the mouse as a model. Murine yersiniosis recapitulates most aspects of disease in humans allowing for a detailed analysis of the pathogenesis. All three pathogenic species of Yersinia have virulence plasmids that are required for full virulence. However, using Y. enterocolitica we have employed a wide variety of techniques to identify numerous virulence factors that are encoded on the chromosome. One of these genes is a transcriptional regulator of the MarR family called rovA. RovA is present in all pathogenic species of Yersinia and has been demonstrated to regulate numerous virulence factors in Y. enterocolitica. The Salmonella homologue of RovA also regulates several virulence factors in Salmonella. Although RovA and SlyA are clearly regulators of virulence, the virulence factors regulated are not the same, suggesting that RovA regulated genes may differ depending on the species. Together these observations lead us to hypothesize that the Y. pestis RovA is a regulator of virulence and that by studying the role of RovA in the virulence of Y. pestis we will gain a greater understanding of the pathogenesis of plague. Specifically we propose: (I) Analysis of the role of RovA in the virulence of Y. pestis, and (2) Identification of the Y. pestis RovA regulated gene products; we predict some of these rovA regulated genes will be unique to Y. pestis (compared to Y. enterocolitica or Salmonella).